The invention relates to ink jet print head components and in particular to heater structures for ink jet print heads.
Thermal ink jet printing involves providing signal impulses to resistive heaters to generate heat, and transferring the heat into adjacently disposed volumes of ink for vaporizing and ejecting the ink through nozzles. As the throughput and print quality continue to increase for ink jet printers, an increased number of ink ejection nozzles and an increased heater firing frequency are required.
Each heater is activated by applying an electrical energy pulse in an amount sufficient to eject a predetermined volume of ink. The xe2x80x9cpulse timexe2x80x9d is the time during which energy is applied to the heater in an amount sufficient to eject ink. The firing interval for a heater consists of the pulse time and dead time, e.g., the time before and after the pulse time when no energy or energy in an amount insufficient to eject ink is applied to the heater. For print heads having an increased number of nozzles and an increased heater firing frequency, the time available to address all nozzle hole positions in an array decreases.
Heater structures typically include heater resistors disposed on a heater chip and one or more protective layers adjacent the heater resistor. The protective layer or layers protect the heater resistors and the heater chip from cavitation and passivation, e.g., mechanical damage from fluid motions of the ink and damage from corrosive/chemical effects of the ink. However, it has been experienced that the protective layers tend to have insulating properties which increase the amount of energy that must be applied to a heater to eject ink at a stable velocity suitable for ink jet printing. The increased energy requirement correspondingly results in an increased pulse time. Also, the increased energy applied to the heater chip can cause heating related problems, such as flooding and poor print quality.
The invention relates to a heater construction that enables a reduction in the pulse time and the energy applied to the heaters, and thus achieves heater structures more suitable for providing ink jet printers having an increased number of ink ejection nozzles and an increased heater firing frequency.
The invention advantageously provides a heater chip structure having heating elements operable at an energy per unit volume of from about 2.9 GJ/m3 to about 4.0 GJ/m3, a pulse time of less than about 0.73 microseconds, and one or more protective layers having a total thickness of less than about 7200 angstroms.
In a preferred embodiment, the heater construction includes a heater chip including a plurality of heating elements. Each heating element includes a heating resistor placeable in electrical communication with a power supply and having an area and a thickness. A protective layer having a thickness of less than about 7200 Angstroms overlies the heating resistor.
Each heating element has a volume and is associated with a corresponding one of the plurality of nozzles, for transferring heat into adjacent ink for a period of time corresponding to a pulse time of less than about 0.73 microseconds to achieve ejection of the ink through the nozzle in response to energy being supplied to the heater resistor by the power supply.
The energy to be supplied to each of the heater resistor ranges from about 2.9 GJ/m3 to about 4.0 GJ/m3 based on the volume of the heating element. The volume of the heating element is determined by the area of the heater resistor multiplied by the sum of the thickness of the heater resistor and the thickness of the protective layer.
In other aspects, the invention relates to ink jet printers incorporating such heater chips, and to methods for printing by use of the heater chips. Use of the heater chips advantageously avoids problems associated with print heads having conventional heater chips, such as undesirable temperature rises and associated effects such as flooding and poor print quality.